Preparation of Mesoporous/Microporous MnCo₂O₄ and Nanocubic MnCr₂O₄ Using a Single Step Solution Combustion Synthesis for Bifunction Oxygen Electrocatalysis

We report the synthesis of mesoporous/microporous MnCo₂O₄ and cubic MnCr₂O₄ using solution combustion synthesis for oxygen reduction and oxygen evolution reactions. XRD and TEM analysis indicate small crystallites of MnCo₂O₄ forming ultra-thin layer of irregular structures that lead to porous morphology. A slightly larger crystallite size was observed for MnCr₂O₄. The surface oxygen defect in MnCo₂O₄ is much higher than MnCr₂O₄ that enhances the active sites for the oxygen adsorption and promotes fast dissociation in presence of more exposed Mn/Co sites during the oxygen electrocatalysis. The electrochemical properties of the synthesized catalysts were analysed using CV, LSV, EIS and CA showing high limiting current density and kinetic current density, positive onset and halfwave potential and higher number of overall electron transfer in MnCo₂O₄ that MnCr₂O₄. Chronoamperometric (CA) runs for 24 h shows excellent stability of MnCo₂O₄ without any significant decrease in the current or potential value in ORR and OER. On basis of the activity and stability performance, MnCo₂O₄ shows to be a promising bifunctional electrocatalyst, with significantly improved performance than previously reported Mn and Co mixed oxides, and comparable to Pt and Ru based catalysts in terms of durability, onset potential and Tafel slope.